siyan

2007 CLK 550

On cold starts, twice now, there seems to be this weird electrical sounding squealing noise. Pretty loud. Seems to be HVAC related (it seems to go away when I turn the HVAC off, but not 100% sure since the squealing is intermittent).

Goes away after 20 seconds or so. Really bizzare. I also heard a similar noise when I had the hood popped (car was even off!) the other day, so I'm wondering if its related.

Really baffled at this one. Any ideas?

Glyn M Ruck

It sounds like the Poly V belt sqealing or a belt tensioner pulley or idler pulley. It could be the swash plate HVAC compressor itself or just the load it places on the belt when selected. You can try an initial spray with belt dressing.

Then I would take off the poly V belt & see if the noise goes away. Do not run the car into overheatig that way!! Only run for a minute or two.

If the noise goes away then check all pulleys including water pump. Pay special attention to tensioner, idlers, alternator & A/C.

Good luck!

siyan

Thanks. Tried it this morning with the engine off actually and still got the noise, although it was much less loud and a lot less duration before it went away.

But I think since the engine was off I can rule out the poly-V belt?

Could it be the AC compressor? Is there a way I can force the compressor to turn on?

Yidney

Is this loud enough or predictable enough that you could post a clip of it? I'm fascinated by a loud squeal with the engine off. You mean totally 100% off? That's a new one. I mean, what runs with the engine off? Not the AC compressor. And it is not your cooling fan still running because it only happens on cold starts. Can you hear it with the hood open and you standing there? If so, where does it sound like it's coming from? If the engine is off, it almost seems like something losing pressure or a vacuum source leaking. Also, can you decribe it better by comparing it to some more common sound? Like fingernails on a chalkboard, Newt Gingrich at a debate, etc. I have to say that an electrical squeal does not bring anything to mind because electricity usually doesn't make noise.

siyan

I can try to get a video tomorrow. Going to leave a camera in the car for this purpose.

Its almost like...the noise you get when you leave a cellphone near a speaker, but higher pitched. Fingers on a chalkboard isn't a bad analogy either, although it is "rougher" than that.

It seems to come from behind the passenger side dashboard.


Regarding the hood up noise:
Actually I now think this (the HVAC noise) is unrelated to the noise I heard when the hood was up, because that was on the other side of the car. Not that having two issues is a good thing though. But yes, when the hood was up the car was off for at least 30 minutes already.

Yidney

Hmmm. What's over there? Your battery. Your ventialtion fan and motor. Not a ton of stuff. Does it last long enough that you can disconect the battery and see if it stops? I'd start removing anything that could muffle the sound like the cabin air filter case to see if that helps pin down the location better.

siyan

You mean disconnect the battery with the engine running or not? Not sure if it will last long enough. I'll have to have a look. I guess I can use a battery keeper in the 12V.

By ventilation fan I assume you mean the main HVAC blower. So the compressor isn't on that side?

Yidney

I meant with the engine off. Maybe the sound does nto last long enough. As for the compressor, you said the sound was more like back near the firewall on the passenger side. The compressor is on the front of the engine down at the bottom and is run by the belt. I can't see how it can make noise with the engne off.

Yidney

And yes, I meant the HVAC blower. It's right behind the battery.

siyan

Gotcha. Seems like things are narrowing down. I'll try and remove some bits to if I can get a better diagnosis.

Thanks Yidney.

romansroad

You might be able to isolate electrical items via the fuse panel, rather than systematically (tediously) actually disconnecting them...just a thought.

siyan

Hm, I'm starting to lean towards the HVAC blower motor. Will try to isolate it further. Haven't had a chance to drive the car the last few days (lots of snow / freezing rain so I took the GLK) but tomorrow...

Glyn M Ruck

Yeah - Dry bearing on the squirrel cage is common. Usually chirps with wind blowing through it with HVAC off though. A number of DIYs on the 203 forum.

Other things that can make a noise with ignition on but engine not running are the Excess Air pump for cold start emissions or the Auxiliary Water pump for heater circulation.

2wheelsoff

having a similar problem and this is driving me crazy...started intermittently and is now consistent.

I located my source of the noise...this is under the speaker on the dashboard passenger side...in a W124 ; to locate remove speaker cover, remove front speaker, disconnect vent hose and shove towards front of car to give you access. there is an electric fan that is connected to a hose - (disconnected in pic from me fishing around). Bearing is dead, as the squeal/ screech goes away when I slow the fan down with finger (not sharp nor powerful fan).


Anyone have any idea what this does? can it be deleted? part # I searched the russian websites parts diagrams but no luck.

Glyn M Ruck

The pic is poor but that looks like the HVAC Duo Valve from older models. If so what you think is a fan is a pump.

kbahl21

Does it sound like a vacumn cleaner?, cuz i have that sound

kbahl21

i know what it is but im to lazy to rip it out lol

2wheelsoff

Will try for a better pic in daylight ...this is inside the firewall, Duo Valve is on the other side in the engine bay... Not sure still what this is...will try and trace it further today.

2wheelsoff

it is #113 in the diagram from link below, but there is no description or part #. looks like it is meant to pump air up to small vent by sunroof controls? or sucks air in for cabin temp to regulate for "auto" feature? Odd.

http://mb.ilcats.ru/part/class/1/cco.../vers//imgno/4

Rudeney

Yes, it's a fan use to supply air to the thermometer for the automatic climate control. Try taking it out and cleaning it. It may jest be full of dust. If that doesn't work, then it will need replacement.

Glyn M Ruck

Ah! OK - understood. It's the old HVAC sniffer fan. With Ya !

Glyn M Ruck

Yidney - your cab looks fabulous!

2ng

is this hvac thing problem common? -excuse the title, I mistook the window while creating a new thread-

siyan

Hmm yes definitely the blower. Got the noise again this morning and it went away right when I hit OFF, and came back when I hit AUTO.

Not annoying enough yet for me to bother much with it, but if/when it gets worse I'll have the dealer handle it.

Worst case...$140 part and some back breaking labour in a few years.

siyan

This vid is going to the dealer.